diff --git a/FindGnss-converters.cmake b/FindGnss-converters.cmake
index cda9bed..1556866 100644
--- a/FindGnss-converters.cmake
+++ b/FindGnss-converters.cmake
@@ -2,5 +2,6 @@ include("GenericFindDependency")
 GenericFindDependency(
     TARGET gnss_converters
     SOURCE_DIR "gnss-converters/c"
+    SYSTEM_HEADER_FILE "gnss-converters/nmea.h"
     SYSTEM_INCLUDES
     )
diff --git a/FindRtcm.cmake b/FindRtcm.cmake
index c1f4bb1..79c9d6b 100644
--- a/FindRtcm.cmake
+++ b/FindRtcm.cmake
@@ -2,5 +2,6 @@ include("GenericFindDependency")
 GenericFindDependency(
     TARGET rtcm
     SOURCE_DIR "c"
+    SYSTEM_HEADER_FILE "rtcm3/bits.h"
     SYSTEM_INCLUDES
     )
diff --git a/FindSwiftnav.cmake b/FindSwiftnav.cmake
index 9c44bfa..7dd65a9 100644
--- a/FindSwiftnav.cmake
+++ b/FindSwiftnav.cmake
@@ -1,5 +1,6 @@
 include("GenericFindDependency")
 GenericFindDependency(
     TARGET swiftnav
+    SYSTEM_HEADER_FILE "swiftnav/bits.h"
     SYSTEM_INCLUDES
     )